1. Technical Field of the Invention
The present invention relates generally to a gas sensor which may be employed in an air-fuel ratio control system for automotive vehicles for measuring the concentration of gas such O.sub.2, NO.sub.x, or CO, and more particularly to an improved structure of such a gas sensor which is designed to provide an air-tight seal for avoiding mixing of the air and a gas to be measured.
2. Background Art
Gas sensors constructed of a sensing element for measuring the concentration of a given gas component and a housing having disposed therein the sensing element hermetically are known. In such gas sensors, an upper portion of the gas sensing element is exposed to an air chamber filled with the air that is a reference gas, while a lower portion of the sensing element is exposed to a gas chamber filled with a gas to be measured.
The above gas sensors, however, have the following disadvantages in manufacturing processes.
The sensing element is usually made of a solid electrolyte ceramic to which electrodes and signal output wires are attached and which has a great strength, but is fragile.
The sensing element is in air-tight engagement with the housing to define the air chamber and the gas chamber so that the gas to be measured may be insulated from the air.
In order to increase the degree of air-tightness between the sensing element and the housing, the sensing element may be press-fitted into the housing, but it may cause the sensing element to be broken. Conversely, the press-fit of the sensing element in the housing is loosened in order to avoid such broken, it may cause the air to be mixed with the gas to be measured, thus resulting in a decrease in measurement accuracy.